More consistent use of mkIte

[langston-barrett]

Many ite constructors in What4.Expr.Builder use mkIte, which encapsulates some trivial rewrites:

what4/what4/src/What4/Expr/Builder.hs

Line 2727 in 038e948

mkIte sym c x y)

what4/what4/src/What4/Expr/Builder.hs

Line 3246 in 038e948

= mkIte sym c x y

what4/what4/src/What4/Expr/Builder.hs

Line 3468 in 038e948

| otherwise -> mkIte sym p x y

what4/what4/src/What4/Expr/Builder.hs

Line 3815 in 038e948

floatIte sym c x y = mkIte sym c x y

but some don't:

what4/what4/src/What4/Expr/Builder.hs

Line 1661 in 038e948

r <- sbMakeExpr sym (BaseIte (SR.semiRingBase sr) sz c xr yr)

what4/what4/src/What4/Expr/Builder.hs

Line 1667 in 038e948

sbMakeExpr sym (BaseIte (SR.semiRingBase sr) sz c x y)

what4/what4/src/What4/Expr/Builder.hs

Line 2179 in 038e948

sbMakeExpr sb $ BaseIte BaseBoolRepr sz c x y

Perhaps worse still, some use it but reimplement its rewrites:

what4/what4/src/What4/Expr/Builder.hs

Lines 3215 to 3219 in 038e948

	structIte sym p x y
	| Just True <- asConstantPred p = return x
	| Just False <- asConstantPred p = return y
	| x == y = return x
	| otherwise = mkIte sym p x y

We should use it consistently.